Work done in the first year of the project evaluating age effects in animal models of extrapyramidal disorders and abnormal behavior has established dose-response functions for apomorphine and d-amphetamine induced behaviors indicatig a hyposensitivity of the mesolimbic system and a possible hypersensitivity of the nigrostriatal system in aged rats. The effect of chronic dopamine agonist/antagonist treatment upon the function of these systems, as indicated by behavior, will be assessed. Manipulation of various neurotrasmitters at specific anatomical loci will be done to determine the contribution of these transmittes to target behavior. Cannulae will be implanted in 3,12, and 24 month old rats at nigrostriatal, mesolimbic, and frontal cortex dopamine system terminals. Dose-response functions for DA, ACh, and GABA agonist and antagonist modification of target behaviors will be established. Behaviors measured will be hyperactivity, hyperreactivity, stereotyped behavior patterns, and tremor. The effects of age on response topography and the shape of the dose-response function for these behaviors will be determined.